1. Field of the Invention
The present invention relates to products, systems, and methods for controlling adult populations of blood-feeding insects, both nuisance pests and vectors of disease. More specifically, this invention relates to methods and systems for attracting multiple species of mosquitoes, for purposes of both population control and monitoring; and for repelling New and Old World sand flies (vectors of leishmaniasis) through the use of a novel combination of floral plant volatile semiochemicals with potent and varied behavioral effects. This semiochemical formulation can be employed in a broad range of means, including a monolithic lure and attractant-impregnated adhesive to be deployed in monitoring traps, and a liquid formulation that can be blended with insecticide to create an attract and kill product amenable to spray application. It is also deployable in larger quantities in strategically placed, self-contained bait stations.
2. Background of the Invention
Insects of all species rely predominately on chemicals detected in their environment for virtually every critical aspect of their lives, from females' selection of appropriate sites upon which to deposit their eggs, location of desirable habitats and food sources and the avoidance of undesirable ones, to the finding and selection of a mate. These behavior-modifying chemicals, known collectively as semiochemicals, have often been used in attempts to manage or suppress insect pest populations through a wide variety of methods, such as mating disruption (artificial treatment of a vulnerable field or environment with synthetic sex pheromone in such a way that the male insect is unable to locate a mate within that field); the placement of an attractant in a monitoring trap or as part of a mass trapping program; repellency, to drive insects away from susceptible host organisms; and attract and kill (A&K), in which an attractant is applied in combination with a killing agent, typically a small quantity of insecticide, to draw insects to a defined location and kill them before they can either reproduce or cause any damage or disease to host organisms.
The pests targeted by the present invention, dipteran hematophagous parasites (those that feed on the blood of humans and animals and in so doing transmit a broad range of blood-borne pathogens), include some of the most harmful insects to the health and prosperity of human populations, both in the U.S. and abroad, that the world has ever known. Mosquitoes transmit some of the most devastating human diseases around the world, such as malaria, arbovirus fevers such as dengue, yellow fever, chikungunya and West Nile virus, and filarial diseases, such as elephantiasis and river blindness among others. Vector-borne diseases transmitted by insects are increasing in prevalence worldwide, and it is likely this trend will only increase in importance as climate patterns change in the future. According to the American Mosquito Control Association, over one million people die from mosquito-borne diseases each year. West Nile virus is currently the mosquito-borne disease (MBD) of greatest concern in the U.S., with over 30,000 human cases reported to the CDC since the disease was first detected in 1999. Historically, several other mosquito-borne diseases, including malaria, yellow fever, and dengue fever, were common killers in the United States. Persistent mosquito control efforts in this country and other industrialized nations have protected their citizens from mosquito-borne illnesses for decades. Although these efforts have been successful in keeping many of us from contracting these illnesses, recent outbreaks of dengue fever, eastern equine encephalitis and the constant threat of West Nile virus are a sobering reminder of the constant necessity for effective, accurate mosquito control and monitoring techniques.
Sand flies also exert harmful impacts on people all over the globe, especially in under-developed regions, as vectors of leishmaniasis, caused by infection with Leishmania parasites. According to estimates by the U.S. Centers for Disease Control and the World Health Organization, leishmaniasis is found in over 90 countries, putting over 310 million people at risk. Approximately 300,000 cases of visceral leishmaniasis, the more severe form of the disease, are reported each year, resulting in over 20,000 deaths. While leishmaniasis is curable with proper treatment, most cases occur in impoverished regions, where access to health care is often limited. No vaccines are available to prevent Leishmania infection. The best method of preventing the disease is to prevent contact between sand flies and their hosts, making effective, low-cost control technologies a major priority in affected areas.
In addition to the impacts biting dipterans have through their capacity to transmit disease, their blood-feeding behavior itself exerts harmful effects on productivity and quality of life for the people and animals they feed upon, particularly for outdoor workers, residents of rural or remote communities, and livestock species. Animals suffering from attacks by large numbers of mosquitoes—under these circumstances, ruminants like cattle and sheep can lose as much as 300 mL of blood in a single day—often do not feed properly, grouping together and attempting to fend off mosquitoes rather than grazing, resulting in decreased weight gains and reduced milk production in dairy cattle. There is a scarcity of recent data attempting to quantify these losses, but older reports estimate economic losses of up to $61 million in a year as a result of mosquito feeding on livestock.
Nuisance biting by hematophagous dipterans also negatively impacts human productivity and prosperity. Aside from the economic opportunity lost if an individual contracts a vector-borne illness on the job, productivity among outdoor workers has been shown to plummet when they are forced to share their work environments with large numbers of mosquitoes. In some cases, agricultural employees may refuse to work where mosquito populations are high. Nuisance mosquitoes may also decrease property values; this is particularly evident in the southeastern U.S. Before the implementation of organized mosquito control efforts in the state of Florida, coastal communities suffered such severe mosquito infestations that they were actually forced to close down during the summer months. Better mosquito control practices have not only fostered better quality of life in these communities, but have also enabled further development of coastal regions, leading to an influx of tourism. There has been found to be a correlation between declining populations of Aedes taeniorhynchus, the saltmarsh mosquito, and increased tourist expenditures.
In light of these impacts, it is little surprise that there is an ever-increasing demand for effective vector control products. The total market size for mosquito adulticides (pesticide products specifically targeting adult insects) alone is estimated at $4.8 billion. More than 352 million acres are managed for vector control by approximately 1800 mosquito control districts and municipalities in the U.S. at an average cost of around $5/acre/day, a market size of approximately $4 billion per year. This is an expanding market, in the U.S. and globally, and is currently dominated by conventional chemical insecticides, particularly by broad-spectrum pyrethroid and organophosphate sprays. Though these types of products have produced good results in the past, delivering a high degree of mortality against multiple species of blood-feeding dipterans, they possess a number of disadvantages that make them an unsustainable pest management solution over the long term, both environmentally and practically. First, as most conventional insecticides kill by contact, they must be blanket sprayed over all surfaces where mosquitoes are thought to be present in order to provide effective population control. This has led to a high degree of public concern regarding the negative effects these chemicals may have on the environment (persistence in the soil, contamination of water supply, spray drift, etc.) and on non-target species (i.e., people, beneficial insects such as pollinators and natural enemies, livestock and companion animals), especially when they are applied near human habitations.
Secondly, as relatively simple chemical toxicants with only a single mode of action, all conventional insecticides developed thus far share a common weakness: the potential for the population of the target insect to become less susceptible—and eventually, all but invulnerable—to them over time. This loss of sensitivity to a particular toxin, called resistance, is more likely to occur when that toxin is applied over a wide area, against multiple consecutive generations of the target insect, and begins when certain individuals within the population, having genes that make them more resilient to the chemical being used, survive exposure to it long enough to produce viable offspring. These offspring then carry these genes on to the next generation, creating the beginnings of a population that is resistant to the toxin.
Another critical component of an effective system of management for biting dipterans is an accurate and timely method of population monitoring. Current monitoring traps tend to rely on a certain class of semiochemicals in order to attract mosquitoes and other blood-feeding insects: host scent cues naturally produced by vertebrates, such as carbon dioxide (CO2), which these insects use to orient toward a potential source for a blood meal. However, traps relying on CO2 as a lure for dipterans can be extremely expensive ($300-$1400 for the initial purchase), cumbersome, and challenging to maintain, requiring a constant supply of electrical or battery power and frequent replenishing of the CO2 source in order to function effectively. They are also inherently limited in their capacity to attract the target insects: CO2 and other attractants designed to mimic the scent profile of a vertebrate host are only attractive to female dipterans seeking a blood meal. Scientists and vector control researchers have long focused on female blood feeding and methods of breaking transmission at this stage, but we believe this is an improper area of emphasis. Blood feeding behavior, despite its importance to mosquitoes' impacts as disease vectors, is actually a comparatively rare event in the insect's life cycle. Female mosquitoes do not require a blood meal to nourish themselves, only to complete development of their eggs, and so are only required to pursue this food source two or three times during their lives, while males do not blood feed at all. A trapping program or an A&K strategy using CO2 or any other vertebrate host cue would therefore only have one or two opportunities to eliminate a mosquito before it becomes capable of transmitting a pathogen (a minimum of two blood meals is required for transmission to occur, one to acquire the pathogen from an infected individual, and one to introduce it to an uninfected individual).
As such, we have designed the current invention to exploit another aspect of hematophagous insect behavior, common to all mosquitoes, both nuisance and vector species, regardless of gender, age, feeding preference, or physiological status: their reliance on sugar solutions to fuel their metabolism. Sugar-based food sources, mainly acquired from flowers and extra-floral nectaries, are absolutely essential in order to sustain the highly active, highly mobile lifestyle that enables mosquitoes and sand flies to survive and reproduce. As such, mosquitoes seek sugar meals on an almost daily basis throughout their lives, relying on floral-produced scent plumes to guide them to appropriate sources of nectar and plant juices, from the time they emerge as adults to the time they die. A female mosquito will engage in this sugar-seeking behavior multiple times before ever pursuing a vertebrate host for blood feeding; she may take from eight to 12 sugar meals prior to her first blood meal, making her far more vulnerable to a floral or sugar-based attractant than to one intended to mimic the scent of a potential blood meal source. A floral plant volatile-based attractant, therefore, would have as many as 10 more opportunities to capture or kill a dipteran vector before it can transmit disease than an attractant meant to manipulate blood-feeding behavior.
Our invention, called Vectrax, is designed as a highly potent and versatile blend of floral attractants and sugar-based phagostimulants that will act as an effective lure for all species of mosquitoes, of either gender, of all physiological states. This invention can be utilized in a wide variety of methods. Vectrax can be deployed alone to substantially improve monitoring efforts for vector mosquitoes of both established and emerging MBDs in the U.S., or blended with small quantities of insecticide to create an attract and kill (A&K) formulation.
For monitoring purposes, this attractant blend could be deployed as a long-lasting monolithic lure, to be placed in virtually any type of trap, or it could be blended directly into the adhesive for a sticky trap. Neither of these trap-lure systems would require a source of power or a CO2 source in order to function, drastically reducing the effort and cost required to deploy and maintain the trap. This enhanced monitoring capacity could help not only to improve strategic timing and location of mosquito control efforts (i.e., identification of key mosquito reproductive sites, targeting of high populations by insecticide sprays), but also improve surveillance of mosquito-borne illnesses, both those already established, and those threatening to invade from foreign regions. Current methods of surveillance of these diseases are to a great extent reliant on case reports of both infected people and animals—a relatively slow and ineffective indicator, at least in terms of informing vector management decisions: mosquitoes responsible for a given case of infection with a mosquito-borne pathogen are likely to be long gone from the area where transmission occurred by the time the case is reported. While mosquitoes collected in CO2 monitoring traps have also been used as a means to track vector-transmitted illnesses, this method of surveillance can also be impractical if the prevalence of the pathogen is low, such as would be the case with a newly introduced pathogen. In such a situation, so few mosquitoes within a given population would carry the disease agent that it would require a very large sample size in order to detect its presence. By increasing both the capacity to attract vector mosquitoes, and the number of monitoring traps that can be placed over the same area within the same time and budget constraints, Vectrax could substantially improve the range and sensitivity of current monitoring programs for established and emerging mosquito-borne illnesses, both within the U.S. and abroad. In addition, while no trap design currently available has demonstrated the capacity to reduce mosquito populations or frequency of biting to any significant degree, the increased potency and decreased cost of the Vectrax attractant compared to CO2 could enable a method of population control by mass trapping, by enabling deployment of traps at a high enough density for an effective mass trapping program.
Vectrax can also be blended with a small quantity of insecticide to create an A&K formulation. Broadly-defined, the A&K technique of pest control consists of attracting adult males, females, or both sexes of a pest species to an insect control agent (e.g., insecticide, sterilant, or insect pathogen). The insect attractant can be a chemical attractant, a visual cue, an acoustic cue, or a combination of these. A highly effective attractant and appropriate insecticide are indispensable ingredients of an effective A&K product. For such a formulation to work, insect pests must be lured to a toxicant, which they must contact and/or feed upon. Contact with the toxicant must then either kill the insect or, at minimum, result in sublethal effects that preclude that insect from effectively performing behaviors that are essential to its survival (feeding behavior, escape responses, etc.), or the survival of its population (effective courtship, mating success). The attractant must be at least as effective, if not more so, as attractants naturally present in the environment, so that the A&K formulation successfully out-competes them and lures the insect pest to the control agent. In many cases, the A&K also contains phagostimulants that induce the insect pest to consume the toxicant formulation. One way for A&K formulations to outcompete existing, natural sources of the stimuli in the treated environment, is by having point sources present at significantly higher densities than the competing natural sources, and/or by being significantly more attractive to the target pest.
Though both methods rely on chemical toxicants to suppress pest populations, A&K techniques present many advantages over cover sprays of conventional insecticides. Attract and kill typically deploys smaller amounts of toxicants, often contained within discrete point sources and coupled to a species specific attractant, reducing the likelihood of negative environmental and non-target effects. There are also substantial economic benefits to the use of A&K over blanket pesticide sprays. Various attempts have been made to describe and quantify the negative impacts that pesticides have on environmental and human health [58], accounting for the combined costs of all pesticides for each country, and not only the costs of individual pesticides at a local scale. For example, Leach and Mumford (2008) developed a simple tool that quickly assesses the indirect costs of individual pesticides based on their particular toxicological and environmental behavior, providing a tool to rapidly estimate the environmental and public health impacts of pesticides in U.S. dollars/hectare/application. The model calculates the cost of a cover spray of Malathion 50% EC at $8.72/ha (this is external cost of an application, not the actual cost of the pesticide) while if the same pesticide were applied as an A&K bait, the cost plummets to $0.04 per ha.
Despite these advantages, with few notable exceptions, the use of formulations baited with phytochemical attractants used by mosquitoes and other biting dipterans to locate sugar meals, remains largely unexplored. Very little is known of the composition of the natural volatile plant semiochemical blends attractive to biting dipterans, and few extracts or synthetic blends of these phytochemicals have been developed for use in vector management formulations.
Furthermore, current A&K formulations lack rainfastness, and sun/UV protection, and consequently have shorter field lives than desired. Their effectiveness is drastically reduced with the incidence of rain, and they invariably leak or drift, contaminating soils and waterways. Current A&K producers frequently create formulations that lack the species selectivity necessary to allow it to be applied in the field without causing environmental or ecological damage. While A&K may be very selective (i.e., if insect sex pheromones are used as attractants), attractants with broad effects, such as plant kairomones, sugar solutions, food fermentation residues, and their combinations, need to be tested for their impact on non-target organisms.
The present invention addresses all these shortcomings in previous A&K strategies targeted toward biting dipterans. Through an extensive series of lab bioassays and semi-field mesocosm (large mosquito-proof greenhouses) trials, we have successfully developed a number of attractant blends that have proven so highly effective against three major vector genera of mosquitoes, Anopheles (vector of malaria, the deadliest MBD of the modern world), Aedes (vector of Dengue fever, one of the most prevalent MBDs in tropical regions), and Culex, (vector of WNV and other arboviruses), that it out-competes natural plant odors and attractants. We have also developed an irresistible phagostimulant blend of sugars and proteins that causes the mosquito to feed continuously on the formulation until it is fully engorged, even when the formulation contains lethal doses of insecticide.
In addition to this high degree of efficacy as a mosquito attractant and phagostimulant, Vectrax also represents a substantial improvement over other forms of mosquito control in terms of safety, affordability, and long-term sustainability. This formulation is composed entirely of organic ingredients, for maximum safety to humans and the environment. As a thick, gel-like material applied in discrete point sources rather than a spray film that covers all surfaces, this A&K formulation is amenable to targeted, strategic application, allowing the user to select application sites that may be expected to have the largest possible impact on the target (areas of high mosquito populations, key mosquito breeding sites, etc.). This method of application reduces the overall quantity of insecticide required to be applied over a given area to achieve and maintain effective control (due to the powerful attraction and phagostimulation that the formulation exerts on the target pests), while eliminating the risk of spray drift and decreasing the likelihood of contamination of the soil or water where it is applied. Vectrax possesses a particularly valuable advantage over other forms of pesticides in that it has demonstrated no negative impacts on the critical pollinator species, Apis mellifera, the honey bee. Vectrax is surprisingly repellent to honey bees and other hymenoptera. Preliminary studies showed that honey bees completely avoided the floral attractant when it was placed in their foraging zones: during 5 minute observations of feeding stations containing 20% sugar solution, we observed an average of 33±5.8 bee visitations. There were zero visitations on feeding stations containing the same 20% sugar solution spiked with a miniscule quantity (0.01%) of our floral attractant.
Vectrax as an A&K solution is a more economically sustainable pest management solution than insecticide cover sprays, as well as a more environmentally friendly one. Aside from requiring a lesser quantity of insecticide to be applied per unit area to achieve effective control, Vectrax can be formulated into a sprayable liquid formulation that will quickly solidify after application, to protect the active ingredients from degradation and extend its field life. This results in a lower frequency of application to maintain mosquito population suppression, reducing the overall cost of the pest control strategy. Furthermore, as an attractant formulation amenable to tank mixing, designed to function in combination with a wide variety of different insecticides, Vectrax is far less susceptible to the development of resistance in the target insects: research has shown that rotation of different insecticides is an effective method of preventing the build-up of resistant pest populations, as the development of resistance to multiple classes of toxins becomes increasingly unlikely. The tank-mixed Vectrax A&K solution can be applied in the field in one of two ways: 1) in relatively large quantities contained within bait stations, which would be particularly useful in areas of high pest population density; and 2) in a large number of much smaller point sources, as applied through manual or mechanical spraying equipment. This manner of application would be of use in areas with lower mosquito population density, as the high density of point sources would dramatically increase the likelihood that the target insects will encounter, respond to, and consume the insecticide-laced formulation.
While this invention was originally developed as an attractant for biting diptera, the floral blend that lends Vectrax its efficacy proved to be extremely complex in chemical composition and behavioral effects, with different compounds eliciting different responses in insects exposed to them. Certain components within this blend have demonstrated a strong repellent effect against New and Old World species of sand flies, opening up a new and unexpected avenue of pest control by means of this invention. Through a series of dual-choice bioassays, a new combination of plant volatile semiochemicals was identified, which acts as a powerful repellent against two vector species of sand flies, Lutzomyia longipalpis and Phlebotomus dubosqui (vectors of leishmaniasis). This semiochemical blend proved more effective against this species than DEET (N, N-diethyl-meta-toluamide), currently considered the gold standard in insect repellents, even when the latter was applied at a substantially higher application rate (1 mg semiochemical blend vs. 1,200 mg DEET), suggesting that our invention has the capacity to repel sand flies more effectively with less material and less cost required than topically applied products like DEET. Female sand flies repelled from host environments will be less likely to obtain a blood meal, reducing egg production, while aggregation by males, which typically occurs near hosts, will also be impeded by the presence of a repellent. Both of these interventions will lead to a decrease in reproductive success within the treated area, and over time, a reduction in sand fly population size.
Regardless of the application method—whether as an attractant for mosquitos or a repellent for sand flies, as an insecticide-free method of pest control or blended with small amounts of reduced-risk toxicants to create a more environmentally sound A&K formulation—this invention will diminish the impacts of biting diptera by a) reducing the frequency of biting events, and consequently, opportunities for vector-borne disease transmission to occur; b) reducing loss of productivity in susceptible livestock due to irritation and blood loss; and c) improve conditions at outdoor work sites, leading to greater worker comfort and productivity. This is highly advantageous in any location where mosquitoes create nuisance and health problems, but is particularly vital in developing areas of the world, where methods of vector-borne pathogen prevention are still largely reliant on indoor interventions (i.e., insecticide-treated bed nets to prevent malaria transmission), leaving outdoor biting events a major source of transmission.